The author studies the demographic problems of the mordva population in the Altai territory using the material basal on statistics and documents. The analysis of numerous statistic data which refer to various periods of the 20th century makes it possible to point out the peculiarities of the demographic development of the mordvaethnic group in Altai and sane other territories of their settlement the results of the population check-up in the 20-21st centuries lay at the basis of ethno-historic reconstruction of demographic processes among the mordva population in Altai.